Vacuum-type circuit interrupter with improved arc splitting means



J. W. PORTER May 25, 1965 VACUUM-TYPE CIRCUIT INTERRUPTER WITH IMPROVED ARC SPLITTING MEANS Filed July 17, 1962 2 Sheets-Sheet 1 F/GJ INVENTOR. JOSEPH W PORTER, m (i ATTORNEY.

May 25, 1965 J. w. PORTER 3,185,797

VACUUM-TYPE CIRCUIT INTERRUPTER WITH IMPROVED ARC SPLITTING MEANS Filed July 17, 1962 2 Sheets-Sheet 2 /NVEN7'0R.' JOSEPH VV. PORTER,

5y Zi m ATTORNEY.

United States Patent 3,185,797 VACUUM-TYPE CIRCUIT INTERRUPTER WITH IMPROVED ARC SPLITTING MEANS Joseph W. Porter, Media, Pa., assignor to General Electric Company, a corporation of New York Filed July 17, 1962, Ser. No. 210,416 12 Claims. (Cl. 200-144) This invention relates to an electric circuit interrupter of the vacuum type and relates more particularly to a circuit interrupter of this type in which the usual circuitinterrupting arc is split into a plurality of series-related arclets that are spun about an axis of the interrupter in order to facilitate interruption.

Previouslyaproposed vacuum interrupters of this type have been relatively complicated and expensive. They have required a relatively large number of components to perform the necessary functions of splitting the are into series-related arclets, spinning these arclets, and shielding the insulation of the interrupter from the arcing products. Moreover, these components have been relatively massive, thus necessitating an enclosure of relatively large diameter for accommodating them.

An object of the present invention is to perform the above described arc-splitting, arc-rotating, and vaporshielding functions with simple and compactly-arranged components that can readily be accommodated in an enclosure of small diameter.

Another object is to reduce the chances that a spark from one electrode to the metallic shield of the interrupter will result in a breakdown between the two electrodes of the interrupter.

In carrying out the invention in one form, a pair of disc-shaped electrodes are provided within a highly evacuated envelope. Between these electrodes there is a main gap across which a circuit-interrupting are is adapted to be established. A-n annular ring surrounds this main gap and has annular arc-running surfaces at its axially opposed sides. Each of these arc-running surfaces is separated from an adjacent electrode by a secondary arcing gap that extends about the outer peripheral portion of the adjacent electrode. The annular ring projects radially inwardly from the envelope and is normally electrically isolated from the electrodes. Means is provided for magnetically driving arcs on to the outer peripheral region of the electrodes and into engagement with the ring to establish series-related arcle-ts across the secondary arcing gaps. The series-related arclets are driven circumferentially about the ring along said arcrunning surfaces by arc-moving means comprising slots extending from the inner periphery of the ring outwardly via paths that have a tangential component relative to said ring. The ring funther comprises means for forcing current flowing through the ring between aligned points on the two arc-running surfaces to follow a path that extends radially-inwardly between the slots and has a net component extending in a direction tangential of said ring.

For a better understanding of my invention, reference may be had to the following description taken in conjunction with the accompanying drawings:

FIG. 1 is a cross sectional view in side elevation of a vacuum type circuit interrupter embodying one form of my invention.

FIG. 2 is a perspective view of one of the contacts or electrodes contained in the interrupter of FIG. 1.

3,185,797 Patented May 25, 1965 FIG. 3 is a sectional View along the line 3-3 of FIG. 1.

FIG. 4 is a sectional view and side elevation of a vacuum type circuit interrupter embodying a modified form of my invention.

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 4.

FIG. 6 illustrates another modified form ofthe invention.

FIG. 7 is a sectional view illustrating another modified form of the invention.

FIG; 8 is a sectional view along the line 88 of BIG. 7.

FIG. 9 is a sectional View illustrating still another modified form of the invention.

FIG. 10 is a sectional view along the line 1(i10 of FIG. 9.

Referring now to the interrupter of FIG. 1, there is shown a highly evacuated envelope .10 comprising a cylindrical casing 11 of insulating material and a pair of metallic end caps 12 and 13 closing off the ends of the casing. The casing 11 is of a vacuum-tight construction and is joined to the end caps by means of suitable seals 14 forming a vacuum-tight connection between the end caps and the casing 11. I

Located within the envelope 1% is a pair of separabl contacts 17 and 18 shown in solid lines in their open circuit or separated position. The upper contact 17 is a stationary contact suitably attached to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower contact 18 is a movable contact joined to a conductive operating rod 18a which is suitably mounted for vertical motion. Upward movement of the contact 18 from its solid line position to its dotted line position engages the contacts and thus closes the interrupter, whereas return movement in a downward direction separates the contacts and opens the interrupter. The operating rod 18a projects through an opening in the lower end cap .13, and a flexible metallic bellows 20 provides a seal about the rod 18a to allow for vertical movement of the rod without impairing the vacuum inside the envelope 10. As shown in FIG. 1, the bellows 26 is secured in sealed relationship at its respective opposite ends to the operating rod 18a and the lower end cap 13.

The contacts 17 and 18 are preferably of the configuration disclosed and claimed in U.S. Patent No. 2,949,520Schneider, assigned to the assignee of the present invention. Accordingly, each contact is of a disc shape and has one of its major surfaces facing the other contact. The central region of each contact is formed with a recess 29 in this major surface and an annular contact-making area 30 surrounds this recess. These annular contact-making regions 30 abut against each other when the lower contact 18a is in its dotted-line, closed position of FIG. 1. These annular regions 30 are of such a diameter that current flowing through the closed contacts follows a loop-shaped path L, as is indicated by the dot-dash lines of FIG. 1. This loop-shaped path has a magnetic effect which tends in a well known manner to lengthen the loop. As a result, when the contacts are separated to form an arc between the areas 30, the magnetic effect of the loop will impel the arc radially outward.

As the terminals of the arc move towards the outer periphery of the discs 17 and 18, the arc is subjected to a circumferentially-acting magnetic force that tends to cause the arc to move circumferentially about the central axes of the discs. This circumferentially-acting magnetic force is preferably produced by series of slots 32 provided in the discs and extending from the outer periphery of the discs radially inward by generally spiral paths, as is shown in FIG. 2, which is a perspective view of the lower contact 18. These slots 32 correspond to similarly designated slots in the aforementioned Schneider patent, and, thus, force the current flowing to or from an arc terminal located at substantially any angular point on the outer peripheral region of the discs to follow a path that has a net component extending generally tangentially with respect to the periphery in the vicinity of the arc. This tangential configuration of the current path causes the magnetic loop L to develop a net tangential force component, which tends to drive the arc in a circumferential direction about the contacts.

Shortly after the terminals of an are have reached the outer periphery of the discs 17 and 18, the arc is divided into two series-related arclets by means of an annular ring 35. This annular ring 35 extends about the longitudinal axis of the interrupter and is supported on the envelope by suitable means such as metallic pins 38 projecting in sealed relationship through the walls of the envelope 10. When the arc is located at the outer periphery of the discs 17 and 18, the radially outwardly acting magnetic force on the arc tends to bow the arc column radially outward into electrical engagement with the ring 35. When this occurs, series-related arcs, referred to hereinafter as arclets, are established between the ring and the two disc contacts 17 and 18, respectively. These arclets are depicted at 40 and 41 in FIG. 1. The gaps across which these arclets extend are referred to hereinafter as secondary gaps. One of these secondary gaps is located between the outer peripheral portion of disc 17 and an annular arc-running surface 36 on the upper side of the ring 35, and the other of the secondary gaps is located between the outer periphery portion of disc contact 18 and an annular arc-running surface 37 on the ring 35. Both of these secondary gaps are of an annular configuration extending about the outer peripheral portion of the disc contacts.

The current-interrupting capacity of an alternating current vacuum circuit interrupter depends upon the rate at which the vacuum can recover its dielectric strength at a current zero following arcing. Generally speaking, the higher this recovery rate, the higher the interrupting capacity. This recovery rate can be increased by reducing the amount of vapors generated by arcing and by accelerating diffusion of the vapors that are generated. For accomplishing these latter two functions, the interrupter is provided with means for spinning the arclets about the longitudinal axis of the interrupter. This spinning action is effected by relying upon a series of slots :4 extending from the radially innermost periphery of the ring 35 radially outward via paths that have a tangential component relative to the ring. These slots 44- are best shown in FIG. 3, which is a sectional view along the line 3--3 of FIG. 1. It will be apparent from FIG. 3 that the slots 44 define fingers 45 located between adjacent slots that have a component extending generally tangentially. When an arc terminal is located on one of these fingers, the current flowing to this terminal through the ring 35 is forced by the slots 44 to follow a path that has a net tangential component relative to the ring in the immediate vicinity of the arc terminal. Such a path is indicated at J in FIG. 3. As a result of this tangential configuration of the current path, there is a loop circuit present which has its arms, designated J and K in FIG. 3, extending circumferentially with respect to the arc 40 interconnecting the arms. This loop circuit has a magnetic effect which tends in a known manner to lengthen the loop, and because the arms of the loop extend circumferentially, this magnetic effect is a circumferentially-acting force that acts in FIG. 3 to drive the arc circumferentially about the axis of the interrupter in a clockwise direction. When an arc terminal has moved clockwise to the end of the finger 45, this circumferentially-acting force drives the arc terminal across the slot 44 to the next finger 45. The current flow to the arc terminal is then concentrated in this next finger 45, and because of the configuration of this finger, there is a new circumferentially-acting loop circuit which continues clockwise motion of the are around the contact periphery. For each of the fingers 45, there is a net circumferentially-acting force component on the arc acting in the same angular direction, and as a result, clockwise motion of the arc continues until the arc is finally extinguished. It will be understood that the fingers 45 are sufliciently close together to enable the arc to be driven across any slot 44 which separates the fingers. It will also be understood that the lower surface 37 of the ring 35 is also intersected by slots corresponding to the slots 44.

It will be apparent from FIG. 3 that the slots 32 in the contact 17 and the slots 44 in the ring 35 force the current at both terminals of the arc to follow paths which have net tangential components and which extend from the arc in the same angular direction. In other Words, both arms I and K of the loop extend from the arc in the same angular or tangential direction. This circuit configuration strengthens the circumferentially-acting magnetic effect on the arc, as compared to that available where there is only one tangential extending arm, thus contributing to higher speed arc motion. Where lower speeds of arc motion can be tolerated, the slots 44 in the ring 35 can be omitted.

It will be noted that the ring 35 contains a circumferentially-extending groove 5t} extending about its entire inner periphery. This groove 59 separates the arc-running surfaces 36 and 37 and is intersected by the tangentially-extending slots 44 at the top and bottom of the ring. One of the purposes of this groove 50 is to force the current flowing between the arc-running surfaces 36 and 37 to follow a path to the are via the finger 45 on which the arc is located rather than a path which bypasses the finger 4-5, as by extend-ing directly between aligned arc terminals on the ring 35. Another purpose of the groove 5% is to force the current paths leading through the ring from arc terminals on the ring to have net components extending in a radially-outward direction from the arc terminals. This radially-outwardly-extending component results in the presence of a magnetic force acting in a direction to prevent the arclets from traveling radially-outward past the ring 35, thus reducing the chances for the arclets to reach the shields 55 and 56, soon to be described.

A factor contributing to the compactness of my interrupter is the fact that the skewed slots 44 extend from the inner periphery of the ring 35 outward. This relationship makes it possible to establish a circumferentiallyacting magnetic force for driving the arc circumferentially about the arc-running surface 36 or 37 as soon as the arclet is established at the inner periphery of the ring 35 and without any need for driving the are further radially-outward. This follows from the fact that the current flowing through ring 35 to an arclet terminal at the inner periphery of ring 35 is forced by the slots 4-4 to follow a path that has a tangential or circumferentiallyacting component which results in a circumferentiallyacting magnetic force for are rotation. The slots 44 are sufficiently close together that this magnetic force is present for substantially all angular positions of the arclet terminal on the inner peripheral portion of ring 35. Since there is no need to drive the arc radially-outward past the inner peripheral portion of ring 35, the ring 35 need not project a substantial distance radially-outward, and this enables me to reduce the diameter of casing 11.

For condensing the metallic vapors that are generated by arcing, two metallic shields 55 and 56 are provided. Each of these shields is an annular member of a generally L-shaped cross section as shown in FIG. 1. The upper shield 55 serves to protect the insulation in the upper half of the interrupter from arc-generated metallic vapors, and the lower shield 56 serves to protect the insulation of the lower half of the interrupter from arc-generated metallic vapors. These vapors travel outwardly from the arcing region via generally straight line paths, and they are intercepted and condensed by these shields 55 and 56 before they can reach the insulation behind the shields.

The two shields 55 and 56 are mounted on the insulating casing 11 by suitable means such as metallic pins 53 extending through the casing in sealed relationship and suitably joined to the shields. The upper shield 55 is electrically isolated from the ring 35 and the contact 17 and is preferably at a voltage approximately midway between the voltage of these two parts when the interrupter is fully open. Similarly, the lower shield 56 is electrically isolated from the ring 35 and the contact 18 and is preferably at a voltage approximately midway between the voltage of these two parts when the interrupter is fully open. The ring 35 is preferably at a potential approximately midway that of the two contacts 17 and 13 when the switch is fully open. The electrical isolation between all these parts is preserved despite the metallic vapors that are generated by arcing since the insulating surfaces that isolate these parts are located behind the shields 55 and 56 and are thus shielded from these vapors.

For increasing the efliectiveness of the shields 55 and 56, a pair of annular recesses .60 are provided in the upper and lower surfaces of the ring 35. One end of each shield fits in one of these recesses 60 with appropriate electrical clearance, but the clearance is small enough to eliminate any continuous straight line path between the arcing regions of the interrupter and the insulating housing. The ring, in effect, overlaps the two shields in a direction axially of the interrupter, thus leaving only a tortuous path between each of the shields and the ring 35.

A particular advantage of the disclosed interrupter is the high dielectric strength available between its opposite electrodes 17 and 18 when the switch is fully open. In this respect, it sometimes happens that a transient high voltage condition will establish a spark between one of the shields and an adjacent electrode. Such a spark can develop into a full scale are with powerfollow current it the shield is electrically connected to the other electrode since in such an arrangement the spark would establish a complete power circuit. Even if the shield is separated from the other electrode by one additional gap, this occasionally may not be enough since the full voltage is applied to this remaining gap once the first gap sparks over, and there is a chance that this remaining gap will break down under this high stress condition before the spark at the first gap is extinguished. I materially reduce the likelihood of a complete power circuit being established by such a spark since our interrupter includes four gaps in series to withstand voltages applied between the electrodes via the shields 55 and de. One of these gaps is between the electrode 17, 17a and the shield 55, another between the shield 55 and the ring 35, stiil another between the ring 35 and the shield 56, and still another between the shield 56 and the eiectrode 18, 184:. Thus, if one of these gaps should break down, there would still remain three gaps in series to withstand the full voltage while the spark persisted.

Another embodiment of my invention is disclosed in FIG4, where parts corresponding to those of PEG. 1 have been given corresponding reference numerals. In FIG. 4 the ring 35 instead of being a part separate from the casing 11 constitutes an integral part of the casing. This ring 35 comprises a cylindrical outer portion 1% and a pair of annular plates 19?. and MP4 brazed at their outer periphery to the outer portion 160. These annular plates 182. and 104 are spaced apart in a direction longitudinally of the axis of the interrupter. The outer cylinder is located between two insulating cylinders 11a and 11b and is suitably sealed thereto at longitudinally opposite ends of the cylinder 100. As shown in FIG. 5, each of the plates 10?. and 1ti4 is provided with slots 44 corresponding to similarly designated slotsin FIG. 3 to provide a magnetic force for driving an arc terminal located thereon circumferentially about the longitudinal axis of the interrupter.

When the contact 18 is driven downwardly from its closed position into the fully opened position of FIG. 4, the are drawn between the portions 30 of the contacts 17 and 13 is driven radially outward into engagement with the inner periphery of the annular plates 102 and 104. This splits the are into series-related arclets extending across secondary arcing gaps of annular configuration extending about the outer peripheral portion of the disc contacts 17 and 18. One of these secondary arcing gaps is located between the upper contact 17 and the upper surface 36 of the annular disc 102, and the other of these gaps is located between the lower contact 18 and the bottom surface 37 of the annular disc 104. The arclets extending across the secondary gaps are indicated at 40 and 41. These arclets are spun about the longitudinal axis of the switch by the magnetic force derived from the slots 44 in the same general manner as described in connection with FIGS. 1-3. The surfaces 36 and 37 on axiallyopposed sides of the ring 35 act as arc-running surfaces during such circumferential motion in the same manner as the correspondingly designated surfaces in FIG. 1. The annularspace between the plates 102 and 104 corresponds to the groove 50 of FIG. 1 and thus forces current flowing between the arc-running surfaces 36 and 37 to follow a path via the finger 45 on which the arc is located rather than a path that bypasses the fingers 45. This path extends between the arc-running surfaces through the cylindrical outer portion 100. In FIG. 4 the plates 102 and 104 are shown projecting radially inwardly beyond the outer periphery of the disc-shaped contacts 17 and 18. This overlapping relationship increases the likelihood that the arc will be split into series-related arclets.

It the plates 1G2 and 104 are to project radially inwardly beyond the outer periphery of the contact discs 17 and 18, it is necessary with the contact arrangement of FIG. 4 that the opposed faces of the discs 17 and 18 taper rather sharply away from each other toward their outer periphery so as to make space available at the outer periphery of the contacts 17 and 18 for the plates 102 and 104. FIG. 6 shows a way of reducing this taper and simplifying the contact shape. The lower contact is divided into'two parts, one a movable part 181) and the other a stationary part 18c that surrounds the movable part 18b. Current flows to and from the movable part 18!) through the rod 181: and flows to and from the stationary part through a tubular conductor 106 when an arc terminal is on the stationary part 180. The two parts 18:: and are electrically connected together by conductive means Hi7, preferably externally of the envelope 10. The movable part 1811 is movable in a vertical direction into and out of engagement with the contact 17 to close and to open the interrupter. When the movable part 1311 is separated from contact 17, the are that is drawn therebetween is driven radially outward by the magnetic edect of the loop circuit L. The lower terminal of the arc transfers to the stationary part 180 and continues moving radially outward until the arc is split into series-related arclets by the plates 102 and 104. The tubular conductor 105 that carries current to the stationary part 1$c is lo cated at the inner periphery of the stationary part so as to accentuate the radially-outwardly acting magnetic force on the are when the lower terminal is on part 180.

In my application Serial No. 184,704, filed April 3, 1962, I disclose and claim a contact arrangement in which one electrode is formed from two relatively-movable parts, one a movable cup-shaped contact and the other a stationary annular arc-runner surrounding the cup-shaped contact and electrically connected thereto. In PEG. 7 l have illustrated how such an electrode structure may be used in an interrupter embodying one form of the present invention. The movable cup-shaped contact is shown at 89 mounted on a movable conductive operating rod 18a, and the surrounding annular arc runner is shown at 82. These parts 80 and 82 are electrically connected together outside the envelope, as schematically indicated at $3. The movable contact 80 is adapted to be moved vertically into and out of engagement with a stationary contact 35. This stationary contact 85 is preferably of a cup-shape similar to that of movable contact 80. Surrounding the stationary contact 85 and electrically connected thereto is an annular arc runner 86 carried by a conductive rod 17a, which also carries the stationary contact 85. The two contacts 80 and 85 are adapted to engage each other when the interrupter is closed at a centrally-disposed point 87 on the longitudinal axes of the two supporting rods 17a and 13a. Each of the cup-shaped contacts St and 35 may be thought of as comprising a base on which contact engagement occurs and a tubular wall portion projecting from the base in a direction away from the location of the other contact. For example, the contact 89 comprises a base 88 and a tubular wall portion 39 projecting away from the base 80 in a direction away from the location of the other contact 85.

Positioned between the two are runners 82 and 36 is a ring 35 corresponding to the ring 35 of PEG. 4. This ring 35 comprises plates 102 and 104 with slots 44 of the same configuration as shown in FIG. cut therein. As will soon be explained, series-related arclets are established during an opening operation between the arc runner 36 and plate fill and between arc runner 82 and plate 104.

Imbedded in the contacts behind the point of contact engagement 87 are two inserts 90 of high resistance metal, e.g., stainless steel, that force the current to follow a path such as shown by the dotted lines L through the contact structure. This path L contains a loop shaped portion immediately adjacent the point 87 which bows to the left, so that when an arc is established at 87 upon contact separation, a magnetic force is present to drive the arc to the left. The upper terminal of the arc transfers to the upper arc runner 86 and the lower terminal runs down the tubular wall 89 establishing arclets 40 and 41.

The arclets 40 and 41 are spun about the longitudinal axis of the interrupter by magnetic forces resulting from the slots 44 in plates 102 and 104 and also by magnetic forces resulting from slots 95 in the two are runners 82 and 86. These slots 95 extend through the entire radial thickness of the arc runners 82 and 36 and intersect the are running surfaces 97 and 98 of the two are runners. The slots 95 in each arc runner extend from this are running surface transversely thereof via paths that make an acute angle with the are running surface. In other words, the slots 95 extend from the arc-running surface by a path that has a net component extending tangentially or circumferentially of the arc runner. This configuration forces the current that flows to or from an arc terminal on the are running surface to follow a path through the arc runner that has a net component extending circumferentially or tangentially of the are running surface. This results in a circumferentially acting force on the arc. The slots 95 in the arc runner 86 depart from the secondary arcing gap in the same angular direction as the slots 44- in the plate m2, and thus both arms of the circumferentially-acting loop circuit extend from the arc in the same angular direction to strengthen the circumferentiallyacting forces on the arc.

Another way in which the ring 35 can be made is illustrated in FIGS. 9 and 10. Here the ring 35 is provided with slots 99 that extend from the arc-running surface 35 or 36 in a direction longitudinally of the interrupter rather than extending radially outward as in the other embodiments. The slots 19 intersecting a given arc-running surface may be thought of as extending transversely of this arc-running surface toward the other arc-running surface. As shown in FIG. 10, the current flowing through the ring 35 to an arc terminal on the arc-running surface 36 or 37 follows a path that has a net component extending circumferentially of the ring in the immediate vicinity of the arc. Even if the arclet 4i and 41 are aligned as shown in FIG. 10, the current flowing through the ring is still forced to follow a path that has a circumferential or tangential component in the immediate vicinity of each arclet. Thus, there is a force to impel each of the arclets circumferentially about the arc-running surface 37 or 36.

It will be noted that the magnetic force for impelling the arclet circumferentially about the arc-running surfaces 37 and 36 of FIGS. 9 and 10 is available as soon as the terminal of the arclet is established at the inner periphery of the ring 35. Even when the arclet terminal is at the inner periphery the current flowing through the ring to the arclet terminal is forced by the slots to follow a path that has a tangential or circumferential component which results in a magnetic force for arc-rotation about the longitudinal axis of the interrupter. The slots are spaced sufficiently close together that this magnetic force is present for substantially all angular positions of the arclet terminal on the inner peripheral portions of ring 35. With the magnetic force for rotating the are being available at the inner periphery of the ring 35, there is no necessity for driving the are further radially-outward. Thus, the ring 35 of PEG. 9 need not project a substantial distance radially-outward, and this enables me to reduce the diameter of the casing ill.

Aside from the ring 55, the parts of the interrupter shown in FIGS. 9 and 10 correspond to similar parts in FIGS. 7 and 8 and have therefore been given corresponding reference characters.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects, and I, therefore, intend in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of my invention.

What 1 claim as new and desire to secure by Letters Patent of the United States is:

l. A vacuum-type electric cirduit interrupter comprising:

(a) a highly evacuated envelope,

(b) a pair of separable contacts of disc configuration disposed within said envelope,

(c) means for separating said contacts to establish an arcing gap therebetween across which an arc is adapted to be established,

(d) an annular ring surrounding said arcing gap and having annular arc-running surfaces at axially-opposed sides of said ring, each of said arc-running surfaces being separated from an adajcent disc contact by a secondary arcing gap that extends about the outer peripheral portion of said adjacent disc contact,

(e) said ring projecting radially inwardly from said envelope and normally being electrically isolated from said contacts,

(1) means for magnetically driving said are on to the outer peripheral region of said contacts and into engagement with said ring to establish series-related arclets across said secondary arcing gaps,

(g) means for causing each of said series-related arclets to move circumferentially about said ring along one of said arc-running surfaces, said aremoving means comprising slots extending from the inner periphery of said ring radially outwardly via paths that have a tangential component relative to said ring,

(/1) and means for forcing current flowing through said ring between aligned points on the two arerunning surfaces near the inner periphery of the ring to follow a path that extends between said slots and has a net component extending in a direction tangential of said ring,

(i) and groove means separating said two arc-running surfaces in the inner peripheral region of said ring for preventing the passage of current between said aligned points via the inner peripheral region of said ring.

2. A vacuum-type circuit interrupter comprising:

(a) a highly evacuated envelope,

(b) a pair of electrodes within said envelope and defining therebetween a main gap across which a circuit interrupting arc is adapted to be established,

(c) an annular ring surrounding said main gap and having annular arc-running surfaces at axiallyopposed sides of said ring, each of said arc-running surfaces being separated from an adjacent electrode by a secondary arcing gap that extends about the outer peripheral portion of said adjacent electrode,

(d) said ring projecting radially-inward from said envelope and normally being electrically isolated from said electrodes,

(e) means for magnetically driving said arc on to the outer peripheral region of said electrodes and into engagement with said ring to establish series-related arclets across said secondary arcing gaps,

(f) arc-moving means for causing said series-related arclets to move circumferentially about said ring along said arc-running surfaces,

(g) said arc-moving means comprising slots in said ring at one of said arc-running surfaces extending from the inner periphery of said ring radially out wardly via paths that have a tangential component relative to said ring,

(it) and means for forcing current flowing through said ring between aligned points on said two arerunning surfaces near the inner periphery of said ring to follow a path that extends from the point on the slotted surface radially outwardly between said slots with a net component extending in a direction tangential of said ring adjacent the point on the slotted arc-running surface,

(1) and groove means separating said two arc-running surfaces in the inner peripheral region of said ring for preventing the passage of current between said aligned points via the inner peripheral region of said ring.

3. The interrupter of claim 2 in which at least one of said electrodes is of a disc-shape and contains slot means extending from its outer periphery inward in such a manner that the current path extending through said one electrode to an arclet terminal located on the outer peripheral region of the electrode has a net component extending generally tangentially with respect to said periphery in the region of said arclet.

4. The interrupter of claim 3 in which the slots in said disc-shaped electrode and said ring extend in the same angular direction from the secondary arching gap between said electrode and ring.

5. The vacuum-type circuit interrupter of claim 2 in which said envelope comprises a hollow casing of insulating material and in which said ring is spaced radially inwardly from said casing and is supported on said casing.

6. The vacuum type circuit interrupter of claim 2 in which said ring has an outer hollow metallic portion through which current flows between the arc-running surfaces of said ring when arclets are present on said arc-running surfaces, said hollow metallic portion constituting a part of said envelope, said envelope further comprising at least two hollow members of insulating material at axially opposed sides of said hollow metallic portion and vacuum tight seals between said hollow insulating members and said hollow metallic portion.

7. The vacuum, interrupter of claim 2 in which said envelope is constructed partially of insulating material and in which there is provided a pair of metallic vaporcondensing shields respectively surrounding said secondary arcing gaps and disposed between said secondary arcing gaps and the insulating portions of said envelope to protect said insulating portions from the condensation of metallic vapors thereon, and means comprising said protected insulating portions for electrically isolating the shield of each secondary arcing gap from said ring and the electrode forming said secondary gap and for electrically isolating said shields from each other.

8. The vacuum circuit interrupter of claim 2 in which said electrodes are of a disc form and contain slots that extend from their outer periphery inward, said slots having a configuration that forces current flowing through each disc electrode from an arclet terminal on said outer peripheral portion to follow a path that has a net component extending generally tangentially with respect to said periphery in the vicinity of the arclet terminal, said latter tangential component extending from the arclet in the same angular direction as the net tangential component of the current path extending from said arclet through said ring.

9. A vacuum-type circuit interrupter comprising:

(Kl) a highly evacuated envelope,

(5) a pair of electrodes within said envelope and defining therebetween a main gap across which a circuit interrupting arc is adapted to be established,

(0) an annular ring surrounding said main gap and having annular arc-running surfaces at axially-opposed sides of said ring, each of said arc-running surfaces being separated from an adjacent electrode by a secondary arcing gap that extends about the outer peripheral portion of said adjacent electrode,

(d) said ring projecting radially-inward from said envelope and normally being electrically isolated from said electrodes,

(e) means for magnetically driving said arc on to the outer peripheral region of said electrodes and into engagement with said ring to establish seriesrelated arclets across said secondary arcing gaps,

(f) and means for forcing the current flowing between arc terminals located on the axially-spaced arc-running surfaces of said ring to follow paths that have net components extending from each of said arclet terminals in a radially-outward direction,

(g) and groove means separating said two arc-running surfaces in the inner peripheral region of said ring for preventing the passage of current between said are terminals via the inner peripheral region of said r1ng.

10. The vacuum type circuit interrupter of claim 9 in which one of said electrodes comprises a first part movable into and out of engagement with the other of said electrodes and a second part surrounding said first part and having an outer periphery that is located adjacent one of the annular arc-running surfaces of said ring on the opposite side of a secondary arcing gap from said annular arc-running surface.

11. The vacuum type circuit interrupter of claim 10,

in combination with arc-moving means for propelling each of said arclets circumferentially aboutsaid ring along one of said arc-running surfaces, said arc-moving means comprising slots extending from the inner periphery of the ring outwardly via paths that have a tangential component relative to said ring.

12. The vacuum-type circuit interrupter of claim 9 in which said electrodes are spaced apart about their 1 1 1 2. outer peripheries when said interrupter is closed and in 2,976,382 3/61 Lee 200-144 which said ring projects inwardly past the outer pe- 3,089,936 5/63 Smith 200-144 ripheries of said electrodes into the space between the FOREIGN PATENTS outer peripheries.

723,123 1/32 France. References fitted by the Examiner 5 UNITED STATES A N ROBERT K. SCHAEFER, Acting Primary Examiner.

2,949,520 8/60 Schneider 200-147 BERNARD A. GILHEANY, Examiner. 

1. A VACUUM-TYPE ELECTRIC CIRCUIT INTERRUPTER COMPRISING: (A) A HIGHLY EVACUATED ENVELOPE, (B) A PAIR OF SEPARABLE CONTACTS OF DISC CONFIGURATION DISPOSED WITHIN SAID ENVELOPE, (C) MEANS FOR SEPARATING SAID CONTACTS TO ESTABLISH AN ARCING GAP THEREBETWEEN ACROSS WHICH AN ARC IS ADAPTED TO BE ESTABLISHED, (D) AN ANNULAR RING SURROUNDING SAID ARCING GAP AND HAVING ANNULAR ARC-RUNNING SURFACES AT AXIALLY-OPPOSED SIDES OF SAID RING, EACH OF SAID ARC-RUNNING SURFACES BEING SEPARATED FROM AN ADJACENT DISC CONTACT BY A SECONDARY ARCING GAP THAT EXTENDS ABOUT THE OUTER PERIPHERAL PORTION OF SAID ADJACENT DISC CONTACT, (E) SAID RING PROJECTING RADIALLY INWARDLY FROM SAID ENVELOPE AND NORMALLY BEING ELECTRICALLY ISOLATED FROM SAID CONTACTS, 